In traditional IP-oriented networks, there are no Quality of Service (QoS) guarantees. This is because traditional internet applications like email or web browsing do not require real-time delivery of packets. The development of IP-based high-demanding real-time applications like IP telephony and multimedia conferencing has lead to the evolution of QoS on the IP networks. In the future, it is expected that Internet Service Providers (ISP) will provide value-added services on their networks to satisfy customer needs. The customers may range from individual users to big telecom service providers or other ISPs.
Monitoring is required for example to maintain and verify contracted packet delivery performance. Conventional techniques for monitoring packet delivery performance include active monitoring, passive monitoring, passive combined monitoring and marking.
The main characteristic of passive (static) monitoring is that it does not change anything in the network traffic but records simple metrics and statistics. Passive monitoring is generally based on Simple Network Management Protocol (SNMP), as described in “A Simple Network Management Protocol (SNMP)”, RFC 1157. Passive monitoring based on SNMP configures and polls Management Information Base (MIB) variables, as described in “Remote Network Monitoring Management Information Base” RFC 2819, in the network elements.
An extension of passive monitoring is when the information collected from multiple points is combined to obtain more complex parameters like available bandwidth or edge-to-edge average drop statistics on a path.
Active probing, or traffic injection, is a group that contains monitoring systems with traffic injecting, processing and replying functionalities. Active-type monitoring actually injects artificial or test traffic into the network. In other words, active monitoring is based on measurements of probe packets injected into the network.
Marking, or packet modification, is a group that includes monitoring systems with packet marking and processing functionalities. This is an active type of monitoring because the marking points modify existing traffic, but it does not generate artificial traffic in the network. Marking-based monitoring systems are able to measure flow-level performance statistics like edge-to-edge average delay, delay variation, packet loss ratios etc.
Conventional monitoring solutions such as those described above are not well suited to modern networks in which it is required to check that packet delivery according to a contracted QoS guarantee is being delivered by the service provider. For example, it is difficult to determine a packet loss indicator over a wide range of time-scales using such techniques.